Spent fuel consolidation system

ABSTRACT

The spent fuel consolidation system provides method and apparatus for remotely vertically and horizontally compacting an array of spent fuel rods while the fuel rods remain submerged in a coolant. The invention comprises a row ordering section for rearranging the configuration of the fuel rods, horizontal consolidation section for horizontally compacting several rows of fuel rods, and a vertical consolidation section for vertically compacting several rows of horizontally compacted fuel rods. The system is capable of compacting the fuel rods from a given fuel assembly to about one half of the volume originally occupied by such fuel rods in the fuel assembly thereby providing greater storage capacity for a given volume of spent fuel storage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to copending United States patentapplication Ser. No. 268,225 filed herewith in the name of P. Pomaibo,et al. and entitled "Spent Fuel Consolidation System" which is assignedto the Westinghouse Electric Corporation.

BACKGROUND OF THE INVENTION

This invention relates to storage of nuclear fuel assemblies and moreparticularly to the consolidation and storage of spent nuclear fuelrods.

After a period of operation of a nuclear reactor, the fuel assembliescomprising the core of the nuclear reactor must be rearranged with thedepleted or spent fuel assemblies being replaced with fresh ones. Thespent fuel assemblies are removed from the reactor vessel and generallystored in a pool of water on the reactor site. Since a conventional fuelassembly comprises structure other than fuel rods such as grids andcontrol rod guide tubes, a spent fuel assembly occupies more space inthe storage pool than would be required for the individual fuel rods.Because the storage pool has a finite volume it would be desirable to beable to store the fuel rods in a closely packed array and with a minimumof support structure to thereby maximize the amount of spent nuclearfuel that can be stored in a given volume of the storage pool. Thiswould provide a greater storage capacity for the spent fuel rods untilthe fuel rods are transported off the reactor site for storage orreprocessing.

However, since the spent fuel rods have been irradiated during reactoroperation, they are highly radioactive and can be handled only by remotemanipulators and while the fuel rods are submerged in a coolant. Theradioactive nature of the spent fuel assemblies increases the difficultyof not only transporting the spent fuel assembly but of also dismantlingthe fuel assembly and storing the spent fuel rods.

Therefore, what is needed is a system for removing the spent fuel rodsfrom a spent fuel assembly and for storing the spent fuel rods in assmall a volume as is possible.

SUMMARY OF THE INVENTION

The spent fuel consolidation system provides method and apparatus forremotely vertically and horizontally compacting an array of spent fuelrods while the fuel rods remain submerged in a coolant. The inventioncomprises a row ordering section for rearranging the configuration ofthe fuel rods, horizontal consolidation section for horizontallycompacting several rows of fuel rods, and a vertical consolidationsection for vertically compacting several rows of horizontally compactedfuel rods. The system is capable of compacting the fuel rods from agiven fuel assembly to about one half of the volume originally occupiedby such fuel rods in the fuel assembly thereby providing greater storagecapacity for a given volume of spent fuel storage.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter of the invention, it isbelieved the invention will be better understood from the followingdescription taken in conjunction with the accompanying drawings,wherein:

FIG. 1 is a view in perspective of the spent fuel consolidation system;

FIG. 2 is a view in perspective of the internal cutter mechanism;

FIG. 3 is a cross-sectional view of the gripper mechanism;

FIGS. 4-6 are views in perspective of the spent fuel consolidationsystem;

FIG. 7 is a partial view in elevation of the consolidation mechanism;

FIG. 8 is a view along line VIII--VIII of FIG. 7;

FIG. 9 is a view along line IX--IX of FIG. 7;

FIG. 10 is a view along line X--X of FIG. 7;

FIG. 11 is a view along line XI--XI of FIG. 10;

FIG. 12 is a view along line XII--XII of FIG. 7;

FIG. 13 is a view along line XIII--XIII of FIG. 7; and

FIG. 14 is a view along line XIV--XIV of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT

When it is desired to consolidate spent fuel rods of a nuclear fuelassembly, it is first necessary to disassemble the fuel assembly andthen rearrange the fuel rods into a compact configuration. The inventiondescribed herein provides a system for removing the fuel rods from thefuel assembly and for remotely rearranging the fuel rods in aconsolidated fashion.

Referring to FIG. 1, the spent fuel consolidation system comprises arotatable platform 20 that is capable of rotating about its verticalaxis under the influence of a drive system (not shown) and that iscapable of operating while completely submerged in a fluid such aswater. Platform 20 comprises a vertical support 22, a fuel assemblystation 24, consolidation station 26 and canister station 28. Fuelassembly station 24, consolidation station 26, and canister station 28are attached to support plate 30 which is rotatably attached to verticalsupport 22. Support plate 30 is arranged such that when it is rotatedabout vertical support 22, fuel assembly station 24, consolidationstation 26 and canister station 28 may be selectively positioned withrespect to gripper mechanism 32 which is slidably mounted on verticalsupport 22. A nozzle removal mechanism 34 is also arranged near platform20 for removing top nozzle 36 from fuel assembly 38. Fuel assembly 38may be one such as that described in U.S. Pat. No. 3,791,466 issued Feb.12, 1974 in the name of J. F. Patterson et al.

In general, fuel assembly station 24 provides a station for holdingspent fuel assembly 38 while top nozzle 36 and spent fuel rods 40 areremoved therefrom. Fuel rods 40 are generally cylindrical metallic tubescontaining nuclear fuel as is well understood in the art. Consolidationstation 26 provides a station for rearranging fuel rods 40 into aclosely packed configuration without the need for the remainder of thefuel assembly support structure. Canister station 28 provides a stationfor locating a canister 42 for accepting and holding fuel rods 40 afterfuel rods 40 have been consolidated by consolidation station 26.

Referring now to FIGS. 1 and 2, nozzle removal mechanism 34 comprises aninternal cutter mechanism 44 that is slidably mounted on positioningmechanism 46. Internal cutter mechanism 44 may comprise a drive mchanism48 with a plurality of internal cutters 50 connected thereto.Positioning mechanism 46 serves to position internal cutter mechanism 44over fuel assembly 38 of fuel assembly station 24. Since the typicalfuel assembly 38 comprises a top nozzle 36 which is attached to aplurality of control rod guide tubes 52, it is necessary to cut controlrod guide tubes 52 so that the upper portion of control rod guide tubes52 and top nozzle 36 may be removed to expose the top ends of the spentfuel rods 40. When internal cutter mechanism 44 is lowered onto topnozzle 36 by positioning mechanism 46, an internal cutter 50 is slidinto each control rod guide tube 52. Once in this position, drivemechanism 48 is activated which causes each internal cutter 50 to rotatein each control rod guide tube 52 and to sever the top section of eachcontrol rod guide tube 52 from the remainder of the control rod guidetube. Positioning mechanism 46 then removes internal cutter mechanism 44from top nozzle 36.

Referring now to FIG. 3, gripper mechanism 32 may comprise a metal firstplate 56, a metal second plate 58 and a flexible member 60 disposedtherebetween. First plate 56 may be connected to a rod 62 that isdisposed through second plate 58 and flexible member 60 and is connectedto an hydraulic cylinder 64. First plate 56, second plate 58, andflexible member 60 have holes therein for accommodating the insertion offuel rods 40 such that when hydraulic cylinder 64 is activated firstplate 56 and second plate 58 are drawn together thereby squeezingflexible member 60, which may be a rubber plate, into contact with fuelrods 40. In this manner, fuel rods 40 may be firmly gripped for removalfrom fuel assembly 38.

Referring to FIG. 4, when top nozzle 36 has been removed from fuelassembly 38, internal cutter mechanism 44 is moved away from fuelassembly station 24 and gripper mechanism 32 is moved downwardly alongvertical member 22 and into contact with the exposed fuel rods 40 offuel assembly 38. Gripper mechanism 32 then grips each fuel rod 40 aspreviously described. With gripper mechanism 32 gripping each fuel rod40, gripper mechanism 32 is moved upwardly along vertical support 22.Since fuel assembly 38 is locked at its lower end to fuel assemblystation 24, the upward pulling of fuel rods 40 by gripper mechanism 32removes fuel rods 40 from the remainder of fuel assembly 38. Inaddition, a cage 66 which may have comb-like fingers may be attached togripper mechanism 32 for maintaining the alignment of fuel rods 40relative to each other. In this manner, fuel rods 40 can be removed fromthe remainder of fuel assembly 38.

Referring now to FIGS. 4, 5 and 6 with gripper mechanism 32 is itsuppermost position, platform 20 may be rotated which will causeconsolidation station 26 to be positioned under gripper mechanism 32 andfuel rods 40. Next, gripper mechanism 32 is lowered along verticalsupport 22 so that fuel rods 40 are inserted into consolidationmechanism 70 of consolidation station 26. Consolidation mechanism 70vertically and horizontal packs fuel rods 40 as fuel rods 40 are loweredinto consolidation mechanism 70 thereby closely packing fuel rods 40.When gripper mechanism 32 has reached its lowermost position, grippermechanism 32 releases fuel rods 40 so that fuel rods 40 are completelycontained in consolidation mechanism 70. Next, gripper mechanism 32 bymeans of a conventional gripper (not shown), is caused to gripconsolidation mechanism 70. While holding consolidation mechanism 70,gripper mechanism 32 is again raised along vertical support 22 untilconsolidation mechanism 70 with the fuel rods 40 therein is raised clearof consolidation station 26. With consolidation mechanism 70 liftedclear of consolidation station 26, platform 20 is again rotated untilcanister station 28 is located under consolidation mechanism 70. Whenconsolidation mechanism 70 is over canister station 28, grippermechanism 32 is lowered thereby positioning consolidation mechanism 70on a canister 72 of canister station 28. With consolidation mechanism 70positioned on canister 72, the bottom end of consolidation mechanism 70is remotely opened thereby depositing fuel rods 40 into canister 72 in aclosely packed fashion. Each canister 72 may be arranged with a dividerso that each canister 72 can hold more than one set of consolidated fuelrods 40. Once fuel rods 40 have been deposited in canister 72,consolidation mechanism 70 may be returned to consolidation station 26by lifting consolidation mechanism 70 and rotating platform 20 in areverse direction.

When consolidation mechanism 70 has been returned to consolidationstation 26 and when the remainder of fuel assembly 38 has been removedfrom fuel assembly station 24, the spent fuel consolidation system isready to accept an additional spent fuel assembly in fuel assemblystation 24. Thus, the system may be used to consolidate several sets offuel rods 40 into a smaller configuration and store them in a singlecanister, while the fuel rods are maintained underwater. When aparticular canister 72 is filled in this manner, the canister may beremotely moved to a spent fuel storage pool for further storage.

Referring now to FIGS. 7-9, consolidation mechanism 70 comprises a rowordering section 80, a horizontal consolidation section 82, and avertical consolidation section 84. Row ordering section 80 comprises afirst frame 86 manufactured from a material such as aluminum forsupporting an array of hollow guide tubes 88. Guide tubes 88 may bestainless steel tubes having a length of approximately 7 feet and havingan inside diameter of approximately 0.50 inches for accommodating theinsertion of fuel rods 40. Guide tubes 88 are arranged in first frame 86to conform to the same arrangement as fuel rods 40 have in a fuelassembly such that when fuel rods 40 are introduced into consolidationmechanism 70 by gripper mechanism 32 each fuel rod 40 slides into aseparate guide tube 88. In addition to guide tubes 88, a plurality ofplugs 90 are disposed between guide tubes 88 in a position to correspondto the positions of a fuel assembly that have no fuel rods such ascontrol rod locations. Plugs 90 serve to maintain alignment of guidetubes 88 and to maintain a configuration corresponding to that of fuelrods 40 in a fuel assembly.

Row ordering section 80 also comprises an aluminum second frame 92 forsupporting the other end of guide tubes 88. However, guide tubes 88 arenot arranged in second frame 92 in the same configuration as in firstframe 86. Rather, some of guide tubes 88 may be slightly curved or bentso as to form a closely packed array of guide tubes 88 as shown in FIG.9. As can be seen from a comparison of FIGS. 8 and 9, guide tubes 88extend from first frame 86 to second frame 92 but the ends of some ofthe guide tubes 88 are arranged in a different configuration in each ofsuch frames. This arrangement of guide tubes 88 provides a means bywhich a set of fuel rods 40 having the same configuration as the fuelrods in a fuel assembly can be introduced in one end of guide tubes 88and moved through guide tubes 88 to exit guide tubes 88 in a moreclosely packed array. It should be noted that not only does theconfiguration in second frame 92 eliminate plugs 90 but it may alsotransform the configuration of first frame 86 from a substantiallysquare array to a substantially rectangular array. Of course, theparticular array chosen for second frame 92 is primarily dependent onthe configuration chosen for the final storage of fuel rods 40. Sincethe length of each fuel rod 40 exceeds the length of each guide tube 88,several of the fuel rods 40 may be slightly bent during its travelthrough guide tubes 88. However, such slight bending is well within theflexibility capabilities of a typical fuel rod 40. Moreover, fuel rods40 can be moved through guide tubes 88 under mere gravitational forcedue to the weight of each fuel rod 40 or they may be pushed throughguide tubes 88 without damage to the fuel rods 40.

Referring now to FIGS. 7, 10 and 11, horizontal consolidation section 82comprises a first housing 94 having a plurality of horizontal stainlesssteel plates 96 attached thereto defining a plurality of horizontalspaces 98 for accommodating fuel rods 40 as fuel rods 40 exit rowordering section 80. A plurality of spacers 100 are attached to firsthousing 94 and are disposed between plates 96 in spaces 98 forcontacting the outermost fuel rod 40 in each space 98. The spacers 100in alternate spaces 98 may be of different lengths for contacting theoutermost fuel rod 40 based on the configuration of fuel rods 40 in eachspace 98. The ends of guide tubes 88 of row ordering section 80 aredisposed in spaces 98 and between plates 96 at first end 102 ofhorizontal consolidation section 82 for introducing fuel rods 40 intothe corresponding space 98. First housing 94 is arranged to have alonger width at first end 102 than at second end 104 so that as fuelrods 40 are moved therethrough, the outermost fuel rod 40 is movedinwardly by contacting spacers 100 thereby horizontally closely packingeach horizontal row of fuel rods 40 while maintaining the verticalspacing between each horizontal row of fuel rods 40 by means of plates96. In this manner, horizontal consolidation section 82 provides a meansto horizontally compact fuel rods 40 as they exit row ordering section80.

Referring to FIGS. 7 and 12-14, vertical consolidation section 84comprises a second housing 106 attached to first housing 94 and arrangedto support plates 96 which extend from first housing 94 into secondhousing 106. As shown in FIG. 12, plates 96 are of different lengths sothat the uppermost plates 96 are shorter than the lowermost plates 96and with the intermediate plates 96 having a length longer than theuppermost plates 96 and shorter than the lowermost plates 96. In thisarrangement, each succeeding plate 96 is generally longer than thepreceding one from top to bottom. In addition, a plurality of rollers108 are mounted on second housing 106 and arranged to contact fuel rods40 as fuel rods 40 exit plates 96. Rollers 108 are attached to secondhousing 106 at different elevations corresponding to the ends of plates96 such that as a row of fuel rods 40 passes beyond the end of a plate96, the fuel rods contact a roller 108 for maintaining the horizontalalignment of the fuel rods 40 and for slightly bending the fuel rodsdownwardly and into contact with the next row of fuel rods 40. Rollers108 may be formed with grooves 110 for accommodating the shape of fuelrods 40 and for maintaining the horizontal alignment of fuel rods 40.

Referring to FIG. 12, as fuel rods 40 are moved through verticalconsolidation section 84, the uppermost row of fuel rods 40 exits plates96 first and contacts a roller 108 that tends to bend fuel rods 40downwardly. As fuel rods 40 proceed through vertical consolidationsection 84, each consecutive horizontal row of fuel rods 40 exits plates96 and contacts an adjacent row of fuel rods 40 with the uppermost rowof fuel rods in contact with a roller 108. With each succeeding roller108 in a lower vertical location with respect to second housing 106 andwith respect to fuel rods 40, rollers 108 cause fuel rods 40 to bevertically compacted until fuel rods 40 exit vertical consolidationsection 84 in a configuration as shown in FIG. 14. In this manner,vertical consolidation section 84 provides a means to verticallyconsolidate fuel rods 40 as fuel rods 40 exit horizontal consolidationsection 82. Fuel rods 40 thereby exit consolidation mechanism 70 in ahorizontally and vertically closely packed configuration occupyingapproximately half the volume of the original fuel assemblyconfiguration. When in this configuration, fuel rods 40 may be depositedin canister 72 as previously described.

It should be understood that consolidation mechanism 70 can be used withvarious other means for introducing the fuel rods thereinto. Forexample, a horizontally arranged mechanism for sliding fuel rods 40 intoconsolidation mechanism 70 could be equally effective.

Therefore, the invention provides a means to remotely consolidate spentnuclear fuel rods for storage.

We claim:
 1. Apparatus for remotely consolidating nuclear fuel rodscomprising:row ordering means arranged to simultaneously accept aplurality of nuclear fuel rods for rearranging said fuel rods into adifferent configuration without damaging said fuel rods; firstconsolidation means associated with said row ordering means forsimultaneously compacting individual rows of said fuel rods withoutdamaging said fuel rods; and second consolidation means associated withsaid row ordering means for simultaneously compacting a plurality ofsaid fuel rods without damaging said fuel rods.
 2. The apparatusaccording to claim 1 wherein said first consolidation means is connectedto said row ordering means for compacting individual rows of said fuelrods as said fuel rods exit said row ordering means.
 3. The apparatusaccording to claim 2 wherein said first consolidation means is locatedbetween said row ordering means and said second consolidation means andconnected to said second consolidation means.
 4. The apparatus accordingto claim 3 wherein said second consolidation means is arranged to acceptindividual rows of consolidated fuel rods for compacting a plurality ofcompacted fuel rods.
 5. Apparatus for remotely consolidating nuclearfuel rods without damaging said fuel rods comprising:a first frame; asecond frame; a plurality of hollow guide tubes having a first endsupported by said first frame and having said first end arranged in aconfiguration for having a plurality of said fuel rods inserted thereinin a configuration similar to the configuration of said fuel rods in afuel assembly, and having a second end supported by said second frameand having said second end arranged in a closely packed configurationfor rearranging said fuel rods into a closely packed configuration;first consolidation means associated with said guide tubes forcompacting individual rows of said fuel rods; and second consolidationmeans associated with said guide tubes for compacting said fuel rods. 6.The apparatus according to claim 5 wherein at least one of said guidetubes is bent between said first frame and said second frame. 7.Apparatus for remotely consolidating nuclear fuel rods without damagingsaid fuel rods comprising:row ordering means arranged to accept aplurality of nuclear fuel rods for rearranging said fuel rods into adifferent configuration; a first housing disposed near said row orderingmeans; a plurality of first plates disposed in said first housingdefining a plurality of first spaces therebetween for accommodating arow of said fuel rods, said first housing and said first plates beingarranged in a converging manner so that each of said rows of fuel rodsare compacted as said fuel rods are moved therethrough for compactingindividual rows of said fuel rods as said fuel rods exit said rowordering means; and consolidation means disposed near said first housingfor accepting individual rows of compacted fuel rods and for compactinga plurality of compacted fuel rods.
 8. Apparatus for remotelyconsolidating nuclear fuel rods without damaging said fuel rodscomprising:row ordering means arranged to accept a plurality of nuclearfuel rods for rearranging said fuel rods into a different configuration;consolidation means disposed near said row ordering means for compactingindividual rows of said fuel rods as said fuel rods exit said rowordering means; a housing disposed near said consolidation means; aplurality of plates disposed in said housing with each of said plateshaving a different length and defining a plurality of spacestherebetween for accommodating a row of said fuel rods; and a pluralityof rollers disposed in said housing near the ends of said plates forcontacting a row of said fuel rods as said fuel rods emerge from beyondthe end of one of said plates for bending a row of said fuel rods intocontact with an adjacent row of said fuel rods thereby compacting aplurality of rows of said fuel rods.
 9. The apparatus according to claim6 wherein said first consolidation means comprises:a first housing; anda plurality of first plates disposed in said housing defining aplurality of first spaces therebetween for accommodating a row of saidfuel rods, said housing and said first plates being arranged in aconverging manner so that each of said rows of fuel rods are compactedas said fuel rods are moved therethrough.
 10. The apparatus according toclaim 9 wherein said second consolidation means comprises:a secondhousing; a plurality of second plates disposed in said second housingwith each of said second plates having a different length and defining aplurality of second spaces therebetween for accommodating a row of saidfuel rods; and a plurality of rollers disposed in said second housingnear the ends of said second plates for contacting a row of said fuelrods as said fuel rods emerge from beyond the end of one of said secondplates for bending a row of said fuel rods into contact with an adjacentrow of said fuel rods thereby compacting a plurality of rows of saidfuel rods.
 11. A method of remotely consolidating spent nuclear fuelrods without damaging the fuel rods comprising:removing said fuel rodsfrom a fuel assembly; arranging said fuel rods in individualnoncompacted rows; compacting each individual row of said fuel rods intoa plurality of individual compacted rows; and compacting each of saidindividual compacted rows into an array of compacted rows of compactedfuel rods.
 12. The method according to claim 11 wherein said step ofremoving said fuel rods from said fuel assembly comprises removingsubstantially all of said fuel rods from said fuel assembly andmaintaining said fuel rods in substantially the same configuration assaid fuel rods had in said fuel assembly.
 13. The method according toclaim 12 wherein said step of arranging said fuel rods in individualnoncompacted rows comprises inserting said fuel rods into an array ofhollow guide tubes with said guide tubes having its first ends arrangedin a different configuration from its second ends so that moving saidfuel rods through said guide tubes rearranges the configuration of saidfuel rods.
 14. The method according to claim 13 wherein said step ofcompacting each individual row of said fuel rods into a plurality ofindividual compacted rows comprises moving each row of fuel rods througha converging housing thereby compacting each of said rows.
 15. Themethod according to claim 14 wherein a plurality of individual rows offuel rods are simultaneously moved through said converging housing. 16.The method according to claim 15 wherein said step of compacting each ofsaid individual compacted rows into an array of compacted rows ofcompacted fuel rods comprises bending said individual rows into contactwith each other.